Octane number control of distillation column overhead by varying reflux

ABSTRACT

A FRACTIONAL DISTILLATION COLUMN OPERATING AS A GASOLINE SPLITTER IS CONTROLLED BY MEASURING THE OCTANE NUMBER OF THE COLUMN OVERHEAD FRACTION AND ADJUSTING THE REFLUX TO THE COLUMN IN RESPONSE TO THE OCTANE NUMBER. THE OCTANE MEASUREMENT IS EFFECTED BY AN ANALYZER COMPRISING A STABILIZED COOL FLAME GENERATOR WITH SERVO-POSITIONED FLAME FRONT WHICH PROVIDES A REAL TIME OUTPUT SIGNAL INDICATIVE OF SAMPLE OCTANE NUMBER.

/N VEN TONS Walter A. Baja/r By. James H. Mc/ augh/in N I se mmw VilUnited States Patent O OCTANE NUMBER CONTROL OF DISTILLATION COLUMNOVERHEAD BY VARYING REFLUX Walter A. Bajek, Lombard, and James H.McLaughlin,

La Grange, Ill., assignors to Universal Oil Products Company, DesPlaines, lll.

Filed Oct. 22, 1969, Ser. No. 868,459 Int. Cl. B01d 3/42; C10g 7/00 U.S.Cl. 196-132 7 Claims ABSTRACT F THE DISCLOSURE BACKGROUND OF THEINVENTION The invention of this application is a process controlapplication of the hydrocarbon analyzer described in United StatesPatent No. 3,463,613, all the teachings of which, both general andspecific, are incorporated by reference herein.

As set forth in application Ser. No. 471,670, the composition of ahydrocarbon sample can be determined by burning the sample in acombustion tube under conditions to generate therein a stabilized coolflame. The position of the flame front is automatically detected andused to develop a control signal which, in turn, is used to vary acombustion parameter, such as combustion pressure, induction zonetemperature or air flow, in a manner to immobilize the flame frontregardless of changes in composition of the sample. The change in suchcombustion parameter required to immobilize the flame following a changeof sample composition is correlatable with such composition change. Anappropriate read-out device connecting therewith may be calibrated interms of the desired identifying characteristic of the hydrocarbonsample, as, for example, octane number. Such an instrument isconveniently identified as a hydrocarbon analyzer comprising astabilized cool ame generator with a servo-positioned flame front.

The type of analysis effected thereby is not a compound-by-compoundanalysis of the type presented by instruments such as mass spectrometersor vapor phase chromatographs. On the contrary, the analysis isrepresented by a continuous output signal which is responsive to andindicative of hydrocarbon composition and, more specifically, isempirically correlatable with one or more conventional identificationsor specications of petroleum products such as Reid vapor pressure, ASTMor Engler distillations or, for motor fuels, knock characteristics suchas research octane number, motor octane number or composite yof suchoctane numbers.

For the purpose of the present application, the hydrocarbon analyzer isfurther limited to that specific embodiment which is designed to receivea hydrocarbon sample mixture containing predominantly gasoline boilingrange components, and the output signal of which analyzer provides adirect measure of Octane number, i.e. research octane, motor octane or apredetermined composite of the two octane ratings. For brevity, thehydrocarbon analyzer will be referred to in the following descriptionand accompanying drawing simply as an octane monitor.

An `octane monitor based on a stabilized cool flame generator possessesnumerous advantages over convenice tional octane number instruments suchas the CFR engine or automated knock-engine monitoring systems. Amongthese are: elimination of moving parts with corresponding minimalmaintenance and down-time; high accuracy and reproducibility; rapidspeed of response providing a continuous, real-time output;compatibility of output signal with computer or controller inuts;ability to receive and rate gasoline samples of high vapor pressure,e.g. up to as high as 500 p.s.i.g., as well as lower vapor pressuresamples (.5-250 p.s.i.g.). 'Ihese characteristics make the octanemonitor eminently suitable not only for an indicating or recordingfunction, but particularly for a process control function wherein theoctane monitor is the primary sensing element of a closed loop controlsystem comprising 0, 1, 2 or more subloops connected in cascade.

The present invention has as its principal objective the direct controlof octane number of a gasoline splitter column overhead stream. Atypical gasoline splitter is an externally refluxed, multiple tray,fractional distillation column employed to separate the light ends andlower boiling normally liquid gas-oline components from the higherboiling components. The feed to such a column may typically comprise astabilized reformate from a catalytic naphtha hydroreforming unit. Sucha reformate will contain C5 and heavier hydrocarbon constituents, withthe end point dependent upon the original end point of the naphthafraction which was hydroreformed. For example, the reformate which isproduced from a naphtha having a 390 F. end point will typically have anend point in the range of about 440 to 450 F. It is normal tofractionate such a reformate to remove the heavier hydrocarboncomponents. Components boiling at a temperature in excess of about 400F. have a high octane number, but they are predominantly aromatichydrocarbons which are precursers to gum formation during gasolinestorage and they can cause excessive deposition of carbonaceous materialin an automobile engine during combustion. The overhead stream from thegasoline splitter column will thus typically comprise hydrocarbons inthe C5 to 400 F. end point boiling range, and the bottoms stream fromthe column will comprise heavy hydrocarbon constituents boiling above400 F. (As used herein, the term end point and the temperaturesillustrated are those typically dened by laboratory distillation inaccordance with ASTM Method D86.)

By and large it has been the practice to operate such a column mostly inthe dark so far as the octane number of the product overhead fraction isconcerned. That is to say, the column overhead product is manuallysampled perhaps once every eight hour shift or perhaps even only once aday. The samples are picked up and taken to the laboratory where thesample is run and the result is then transmitted back to the unitoperator who, until then, has not been able to ascertain what change, ifany, should have been made at the time the sample was taken. Therefore,to be on the safe side, the unit operator Will usually run the gasolinesplitter column with excessive heat input and with correspondingover-reflux whereby the overhead fraction of the stabilized reformatewill actually be outside of product specifications with respect tooctane number a good part of the time. This method of blind fractionatoroperation clearly increases the reliners costs.

The control problem is further complicated by the not uncommon practiceof using a single fractionation column to process more than one gasolinestream. For example, a single gasoline splitter column will oftenreceive plural or combined feeds which are stabilized reformates fromtwo or more independently operated catalytic naphtha reforming units.yOr the splitter column may be operated on a gasoline feed comprising amixture of stabilized reformate, cat cracked gasoline, natural gasoline,etc. An upset in the operation of a single such reformer (or othersimilar gasoline feed source) will carry through to the gasolinesplitter and be reflected in olfspecication product since the splittercolumn overhead product is no longer indicative of only the operation ofa single reformer or other gasoline source. Continuously meeting octanenumber specification is, therefore, an exceedingly diflicult andhaphazard task when employing a single splitter column to handle such aplurality of gasoline streams.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide an improved control system for use and incombination with a continuous flow reliuxed fractional distillationcolumn.

It is another object of the present invention to provide such animproved control system for a fractional distillation column operatingon one or more stabilized gasoline feed stocks.

It is a further object of the present invention to provide an improvedcontrol system for maintaining such a fractional distillation columnunder operating conditions sufcient to produce an overhead fractioncomprising a gasoline product having a substantially constantpredetermined octane number.

These and other objectives of the present invention, as well as theadvantages thereof, will be more clearly understood as the invention ismore particularly disclosed hereinafter.

In accordance with the present invention, the octane monitor comprisinga stabilized cool llame generator with servo-positioned ame front isconnected to receive a continuous sample of the splitter column overheadproduct. The output signal of the octane monitor, which can be, andpreferably is, calibrated directly in terms of octane number, isutilized-to reset or adjust the rate of ow of reflux to therectification section of the column so that the octane number of the netoverhead fraction is maintained at a substantially constantpredetermined level. This control system assures that the overheadgasoline product is always on specification, regardless of upsets ordisturbances, and further effects a savings in utility costs in that thesplitter column may thereby be operated at minimum heat input andminimum reflux.

Because there is a direct measurement and control of octane rating, thiscontrol system is to be distinguished from those prior art controlsystems wherein some composition property, such as percent aromatics orconductivity or dielectric constant, is measured and controlled, all ofthese latter properties being merely an indirect indication of octanerating which is only narrowly correlatable therewith. Such indirectcorrelation becomes invalid for any significant deviation from thedesign control point.

The control system of this invention is also to be distinguished fromthose prior art systems employing automated knock-engines as the octanemeasuring device. The instant octane monitor is compact in size, can betotally enclosed by an explosion-proof housing and therefore can be usedin hazardous locations. In fact it is normally fieldinstalledimmediately adjacent to the gasoline splitter column. A knock-engine,however, cannot be employed in hazardous locations and must therefore besituated remote from the sample point.

'Ihe sample transport lag or dead time of a closecoupled octane monitorlis typically of the order of two minutes, and its 90% response time isanother two minutes. This is a very good approach to an essentiallyinstantaneous or real time output. By way of contrast, the transport lagalone of a knock-engine may be of the orderof thirty minutes or more,which those skilled in the control system art will recognize to |be asubstantial departure from real time output. With that much dead timebuilt into a closed loop, it is extremely diflicult to achieve andmaintain stability. The injection of an outside disturbance of anyappreciable magnitude, in such a potentially unstable system, will oftenresult in undampened cycling with the consequence that the system willhave to be put on manual control.

In a broad embodiment, the present invention is directed to a controlsystem for use and in combination with a continuous ilow, fractionaldistillation column, the feed to which is a gasoline fraction, theoverhead from which comprises the lower boiling components of saidfraction and the bottoms from which comprises the higher boilingcomponents of said fraction, said column including a rectilication zonehaving a reflux conduit means in communication therewith at a iirstlocus and meansv to supply reflux to said reilux conduit means, saidcontrol system for said column comprising: (a) means operativelyassociated with said reux conduit means to vary the flow of reflux tosaid rectification zone; (b) a hydrocarbon analyzer comprising astabilized cool flame generator with a servo-positioned flame frontcontinuously receiving a sample of said column overhead and developingan output signal which in turn provides a measure of sample octanenumber; and, (c) means transmitting said analyzer output signal to saidreflux ow varying means (a) whereby the flow of reflux to said column isregulated responsive to octane number of said column overhead and saidoctane number is thereby maintained at a substantially constantpredetermined level.

Preferred specific embodiments will incorporate one or more cascadedsubloops which more immediately control the reflux liow to the column.For example, there may be a flow control loop on the reliux line to therectification section of the column, the octane monitor output thenbeing cascaded to the flow controller setpoint. Alternately,rectification section temperature control may reset the ow controllerand the octane monitor output will reset such temperature controllersetpoint. Other embodiments will become apparent in light of thedetailed description of the invention.

The invention may now be more clearly understood by reference to theaccompanying drawing which illustrates a typical splitter columntogether with one mode of controlling the flow of reflux thereto in amanner sufficient to maintain constant octane number on the overheadproduct.

DESCRIPTION OF THE DRAWING With reference now to the drawing, there isshown a gasoline splitter column 4 receiving a plurality of stabilizedgasoline feeds. Splitter column 4 is a conventional continuous owexternally reuxed fractional distillation column containing from l0 to50 or more vertically spaced vapor-liquid contacting stages as, forexample, bubble decks, sieve decks, preforated trays or the like. Line 1carries a Feed No. 1 comprising stabilized reformate from the stabilizercolumn of a naphtha reforming unit No. 1. Line 2 carries Feed No. 2comprising stabilized reformate from the stabilizer column of a naphthareforming unit No. 2. The combined reformates are charged to the column4 via line 3 which connects with the column at a locus approximatelymidway in the height thereof. A plurality of vapor-liquid contact stagesabove this locus comprises the rectification zone S and a plurality ofcontact stages below the locus comprises the stripping zone'6 of thecolumn.

The two reforming units are separate, independently operated catalyticnaphtha reforming units; the details thereof form no part of the presentinvention, being conventional and well known in the art. A typicalcatalytic naphtha hydroreforming unit is described in U.S. Patent3,296,118 (Class 208-) to which reference may be had for specificinformation concerning ow arrangement, catalyst, conditions etc. Thefeed to column 4 is generally under stabilizer reboiler level controlfrom the preceding reforming units rather than direct ow control.Accordingly, the feed rate is usually, but not always, relativelyconstant, but it may be subject to some variation due to changes innaphtha feed composition, catalyst and/or operating conditions in eitheror both of the catalytic reforming unit reaction zones, or due tochanges in operating conditions of the reforming unit stabilizercolumns.

Gasoline splitter column 4 is maintained under operating conditionssufficient to separate the combined reformate feed stock into anoverhead gasoline fraction having an end boiling point of about 400 F.and a bottoms fraction comprising heavy hydrocarbon constituents of thecombined reformate feed having a boiling range of from about 400 F. toabout 550 F., or even higher. While the refiner will typically setcontrol of splitter column 4 to produce an overhead fraction having anend point of about 400 F., this is only a secondary consideration. Theprimary consideration is normally to produce an overhead fraction havingan octane number of predetermined value, and this octane number is theprimary control for operation of the column 4. Any deviation of octanenumber will require a compensating deviation of endpoint in order toproduce an overhead product of constant octane number.

In order to accomplish the desired separation, the gasoline splittercolumn 4 will contain the rectification zone 5 and the stripping zone 6,as indicated hereinabove, in order that the most effective and efficientseparation of hydrocarbon constituents may be accomplished within thefractionating column. In addition to the rectification and strippingzones, the column is provided with a reboiling section for heat input,and an overhead section which provides reflux liquid in a manner whichshall be set forth hereinafter.

The reboiler section of fractionating column 4 comprises a reboilerliquid line 7, a reboiler heat exchanger 8, and a reboiler vapor returnline 9 which are of conventional construction and design. Conventionalinstrumentation, not shown, is provided to control the heat input to thereboiler system. In addition, gasoline splitter column 4 is providedwith a bottoms fraction draw-off line 10, whereby the heavy gasolineproduct may be withdrawn and sent to storage or to other processing.

The desired gasoline constituents of the combined reformate feed whichis introduced into splitter column 4, are withdrawn in a vapor phasefrom column 4 via line 11 and passed to a heat exchanger 12 wherein theyare condensed and cooled to about 100 F. or less. The condensed andcooled gasoline fraction passes from the heat exchanger 12 via line 13into a fractionator overhead receiver 14 which is typically maintainedat a pressure of from about 5 to 100 p.s.i.g., or more, in order tomaintain low boiling constituents within the liquid phase. The liquidaccumulated in the overhead receiver 14 is separated into two portions.A first portion is withdrawn via line 15 as a light gasoline product andsent to storage facilities, not shown. This light gasoline producttypically will have a boiling range of from about C5 to about 400 -F. asindicated by ASTM Method D-86.

The second portion of the condensed overhead is withdrawn from theoverhead receiver 14 via line 16 as the reflux which is returned to thecolumn 4 in order to maintain the proper degree of vapor rectificationwithin zone 5. The refiux conduit 16 also contains therein a flowmeasuring means such as an orifice 17 and a flow controlling means suchas control valve 18. The reflux iiow rate is regulated by a flow controlloop comprising the orifice 17, a flow signal line 19, a flow controller20, a controller output line 21, and the control valve 18. The set pointof fiow controller 20 is automatically adjustable.

A temperature controller 23, also provided with an automaticallyadjustable set point, senses and controls the rectification zonetemperature as detected by a thermocouple or other sensing means 24located within the rectification zone at a locus below the reux inlet ofthe column. The resulting temperature output signal is transmitted fromthe temperature controller 23 via controller output line 25 to adjust orreset the setpoint of flow controller 20.

Octane monitor 26, utilizing a stabilized cool flame generator withservo-positioned flame front, is `fieldinstalled adjacent column 4. In apreferred embodiment, the flows of oxidizer (air) and fuel (gasolinesample) are fixed as is the induction zone temperature. Combustionpressure is the parameter which is varied in a manner to immobilize thestabilized cool flame front. Upon a change in sample octane number, thechange in pressure required to immobilize the flame front provides adirect indication of the change in octane number. Typical operatingconditions for the octane monitor are:

Air flow-3500 cc./min. (STP) Fuel flow-l cc./min.

Induction zone temperature-700 F. (Research octane), 800 F. (motoroctane) Combustion pressure-4-20 psig;

Octane range (maX.)--102 1 1 The actual calibrated span of the octanemonitor as here utilized will, ln general, be considerably narrower. Forexample, 1f the target octane is 95 clear (research method), a suitablespan may be 92-98 research octane. When a relatively narrow span isemployed, the change in octane number is essentially directlyproportional to the ohlange in combustron pressure.

Dashed line 27 represents a suitable sampling system to provide acontinuous sample of column overhead to the octane monitor. For example,the sampling system 27 may comprise a sample loop taking the lightgasoline product at a rate of cc. per minute from a point upstream of acontrol valve and returning it to a point downstream from the controlvalve, the sample itself ibeing drawn off from an intermediate portionof the sample loop and injected at a controlled rate by a metering pumpto the combustion tube of the octane monitor. The octane monitor outputsignal is transmitted via line 28 to the setpoint of temperaturecontroller 23. This may be a direct field connection, but preferably theoctane monitor out-put will first be sent to an octanecontrollerrecorder located in the refinery control house, with thecontrol signal therefrom then being set to reset the setpoint oftemperature controller 23 which may be a ternperature recordingcontroller also located in the control house.

PREFERRED EMBODIMENTS As indicated above, one preferred embodiment ofthe present invention consists of the application of the inventivecontrol system in the splitting of reformate gasolines. As previouslynoted, the heavy ends of such reformate gasolines are high in octanenumber due to the fact that high boiling aromatic constituents areconcentrated in the heavy end of the reformate. In splitting reformatesto make various boiling range fractions, it is generally found that theoctane number of the heavy gasoline product which is withdrawn via line10 is consistently higher than the octane number of the light gasolineproduct which is withdrawn via line 15. This correlation of octanenumber with gasoline fraction is found to occur even when as little as 5volume percent or as much as 60 volume percent of the reformate gasolineis removed as a bottoms product via line 10.

Thus, when operating column 4 on a reformate feed stock, any decrease inthe measured octane number of the ovrhead product indicates that aninsufficient amount of heavy boiling components is being withdrawn as aportion of the overhead product. In order to compensate for thiscondition, the octane monitor 26 will call for an increase in therectification zone temperature in order to include a greater portion ofthe high octane number heavy ends in the overhead vapor which leavescolumn 4 via line 11. Temperature controller 23, being reset by theoctane monitor, will then call for a decrease in reflux flow which inturn will be effected by fiow controller 20 and control valve 18.

7 Again, when operating column 4 on a reformate feed stock, an increasein the measured octane number of the overhead product is an indicationthat an excess of high octane number heavy ends is being withdrawn fromcolumn 4 in the overhead fraction. The octane monitor 26 therefore willcall for a decrease in the rectification zone temperature in order toeliminate a greater portion of the heavy ends-from the overhead Vapor.Temperature controller 23 being reset by the octane monitor will callfor an increase in the reflux flow which in turn will be effected byflow controller 20 and control valve 18.

'I'hose skilled in the art realize, of course, that a gasoline splittercolumn such as column 4 does not always operate on a feed stockcomprising reformate gasoline. In many instances splitter column 4 mayoperate to separate an overhead and a bottoms fraction from a gasolinefeed stock which may comprise one or more gasolines such as crackedgasoline, natural gasoline, alkylate gasoline, etc., and the feed stockmay comprise stabilized and unstabilized gasolines which may includedebutanized, depentanized, and dehexanized gasolines. Thus, it ispossible that there will be embodiments of operation wherein the heavy:gasoline product withdrawn via line 10 will have an octane number whichis consistently lower than the octane number of the light gasolineproduct Withdrawn via line 15. In those instances, the octane monitor 26will call for overall corrective action which will be the reverse ofthat which has been indicated hereinabove for operations on reformatefeed stocks. That is to say, if the overhead product of line ,15indicates a decrease in themeasured octane number, this would be anindication that an excessive amount of low octane hea-Vy ends is beingwithdrawn overhead via line 1\1, and the control system would functionto increase the amount of reflux in order to eliminate a greater portionof the heavy ends from the overhead vapor. On the other hand, if anincrease in the measured octane number of the overhead product isindicated, then the octane monitor 26 would compensate by calling for adecrease in the amount of reflux to column 4 in order to allow a greaterportion of the low octane heavy ends in the overhead vapor leaving vialine 11.

Those skilled in the art will readily ascertain the proper direction ofcorrective action which is to be taken in the inventive control systemfor any specific gasoline feed stock composition and any specificfractionation cut-point from the teachings which have now been presentedhereinabove.

Those skilled in the art realize, of course, that thermocouple 24 couldbe placed in locations other than that shown as, for example, in vaporoutlet line 11. The drawing, however, illustrates a preferred embodimentwherein the temperature controller 23 senses and controls not theoverhead vapor as it emerges directly from column 4, but rather theliquid or vapor temperature obtaining within the rectification zone at apoint some distance below the reflux inlet of line 16 and above the feedinlet of line 3. In this preferred embodiment, the thermocouple 24 istypically located several trays (for example 2-6 trays) below the refluxinlet of line 16. This arrangement will afford a more immediatedetection of changing heavy ends concentration, at least several minutesbefore such heavy ends reach the overhead vapor line 11 to cause achange ln the octane number of the overhead product.

While the double cascade arrangement illustrated in the drawingrepresents a preferred embodiment, it is within the scope of thisinvention to omit the temperature controller 23 and to reset iiowcontroller 20 directly by the octane monitor output signal transmittedvia line 28. Alternatively, the flow controller 20 could also beomitted, in which case octane monitor output signal line 28 wouldconnect directly with valve 18. It may be expected, however, thatelimination of either or both of the subloops will result in somewhatpoor overall control because rectification zone temperature and refluxow variations will become a source of additional upsets, and alsobecause the relatively large time constant of the stabilizer columnitself tends to make single loop control unstable.

Although the inventive control system has been disclosed relative to theseparation of a gasoline fraction to produce an overhead fraction havingan end boiling point of about 400 F. and a bottoms fraction containingheavier hydrocarbon constituents, the invention is not so limited. Thecontrol system is clearly applicable to any distillation wherein agasoline fraction is separated into an overhead containing the lowerboiling components of the fraction and a bottoms containing the higherboiling components of the fraction, regardless of the distillationcut-point between the fractions. As used herein, the term higher boilingcomponents refers to those hydrocarbon constituents which boil at atemperature above the distillation cutpoint for the overhead fraction.Thus, if the fractional distillation is undertaken to produce anoverhead gasoline having an endpoint of, say, 380 F., the higher boilingcomponents will comprise the bottoms fraction of the distillation. Andif the distillation is undertaken to dehexanize the gasoline feed, thehigher boiling components comprise hydrocarbons having seven or morecarbon atoms per molecule. Similarly, the term lower boiling componentsrefers to those hydrocarbon constituents which boil at a temperaturebelow the distillation cut-point.

The invention claimed:

1. In combination with a continuous ow fractional distillation column,the feed to which comprises a gasoline fraction, the overhead from whichcomprises the lower boiling components of said fraction and the bottomsfrom which comprises the higher boiling components of said fraction,said column including a rectification zone having a reflux conduit meansin communication therewith at a first locus and means to supply refluxto said reflux conduit means, a control system for said columncomprising:

(a) means operatively associated with said reflux conduit means to varythe flow of reflux to said rectification zone;

(b) a hydrocarbon analyzer comprising a stabilized cool flame generatorwith a servo-positioned ame front continuously receiving a sample ofsaid column overhead and developing an output signal which in turiprovides a measure of sample octane number; an

(c) means transmitting said analyzer output signal to said reflux flowvarying means (a) whereby the flow of reux to said rectification zone isregulated responsive to octane number of said column overhead and saidoctane number is thereby maintained at a substantially constantpredetermined level.

2. The system of claim 1 wherein the feed to said column comprises atleast one stabilized gasoline fraction.

3. The system of claim 1 wherein said reflux flow varying meanscomprises a flow control loop including a flow controller having anadjustable setpoint regulating the rate of flow of reiiux through saidreflux condition means, said setpoint being adjusted in response to saidanalyzer output signal.

4. The system of claim 3 further characterized in the provision of meansto sense the temperature in said column at a second locus, temperaturecontrol means having an adjustable set point connecting with saidtemperature sensing means and developing a temperature output signal,said means transmitting the last-mentioned output signal to the setpointof said flow controller, said means (c) transmitting said analyzeroutput signal to the temperature controller setpoint whereby the latteris adjusted responsive to overhead octane number.

5. The system of claim 4 wherein said temperature sensing means islocated in said rectification zone.

6. The system of claim 5 wherein said second locus is below said -iirstlocus.

7. T he system of claim 6 wherein said distillation column contains aplurality of fractionation trays and said temperature sensing means islocated several trays below said rst locus.

10 3,463,725 8/ 1969 Macfarlane et al. 203--3 X 3,475,288 10/ 1969Ezzell 203-3 X References Cited UNITED NORMAN YUDKOFF, Primary Examiner5 D. EDWARDS, Assistant Examiner STATES PATENTS Berger 203,--3 X Lupferet al 203-3 X -Rijnsdorp 203-3 x U'S' Cl' X'R' Rijnsdorp et al. 203--3 X196100; 202-160; 203-3, Dig. 18, 2; 20S-Dig. 1,

Fenske et al. 23-253 X 10 358

